The present document is related to and claims priority on Japanese priority documents JP11-310352 and JP 2000-259878 filed in the Japanese Patent Office on Oct. 24, 1999, and Aug. 29, 2000, respectively, the entire contents of which are hereby incorporated herein by reference.
1. Field of the Invention
The present invention relates to antennas incorporated into various apparatuses, such as various communication apparatuses for transmitting and receiving radio waves, which have functions of transmitting and receiving radio waves.
2. Description of the Related Art
Recently, various apparatuses, such as communications apparatuses for transmitting and receiving radio waves, which have functions of transmitting and receiving radio waves in a broad sense, are in increasing demand. Accordingly, an increasing number of antennas used within a frequency band from a few hundreds of MHz to a few GHz have been employed. These antennas are used in, for example, mobile communication, next-generation transportation systems, and non-contact cards used in automatic ticket readers. Methods for performing wireless data communication without using long, burdensome cables have been introduced, including wireless communication between cordless Internet appliances, wireless local area networks (LAN), and for Bluetooth. The above antennas are expected to be widely used in these fields. Such antennas are also used in wireless data transmission and reception from various terminals. The demand for antennas is increasing in the fields of telemetering for communicating safety management information concerning waterworks and gas systems by radio waves, point-of-sale (POS) systems for banking terminals, and the like. Moreover, such antennas are applicable to home appliances including televisions, such as portable satellite broadcasting receivers, and for automatic vending machines. The range of uses of such antennas is very broad.
As antennas for use in apparatuses having functions of transmitting and receiving radio waves, retractable monopole antennas, which are mounted on casings of apparatuses, are mainly used. In addition, helical antennas, which slightly protrude to the outside of the casings, are known.
The background antennas, such as monopole antennas, are disadvantageous in that it is burdensome to handle monopole antennas and in that monopole antennas are easily damaged since they are required to be extended during used. Helical antennas are disadvantageous in that, since antenna elements formed of air core coils are protected by covering materials such as a resin, the outer dimensions tend to be greater. When helical antennas are fixed so that they protrude from casings, the overall appearance is not satisfactory.
In order to address the above mentioned and other problems, it is an object of the present invention to provide a small antenna to be attached to the interior of a casing of various types of apparatuses, including various communication apparatuses for transmitting and receiving radio waves, which have functions of transmitting and receiving radio waves, so that it is not necessary to extend the antenna, so that the antenna is not easily damaged, and so that the overall appearance of the apparatuses is not worsened.
According to an aspect of the present invention, an antenna is provided including a plurality of bases stacked in the thickness direction. Conductor patterns are formed on the bases, and conducting sections for electrically interconnecting the conductor patterns are formed on the bases. The conductor patterns form inductance components and capacitance components.
With such a configuration, a resonant system required to transmit and receive radio waves is configured with the inductance components and the capacitance components, and hence the resonant system functions as an antenna.
Among the conductor patterns formed on the bases, a capacitance component may be constructed of a conductor pattern formed on a first base and a conductor pattern formed on a second base. An inductance component may be constructed of at least one of those two conductor patterns. The capacitance component and the inductance component may be connected in parallel.
With such a configuration, the capacitance component and the inductance component formed of the conductor patterns are connected in parallel to form the resonant system required to transmit and receive radio waves, which functions as the antenna.
The conductor patterns may include capacitance patterns and inductance patterns. Among the bases, an inductance pattern may be formed on a first base. A first capacitance pattern may be formed on a second base adjoining the first base. A second capacitance pattern, which is opposed to the first capacitance pattern to form a capacitance component, may be formed on a third base adjoining the second base. The inductance pattern and the capacitance component formed by the first and the second capacitance patterns may be connected in parallel by the connecting section.
With such an arrangement, the capacitance component and the inductance component formed of the conductor patterns are connected in parallel to form the resonant system required to transmit and receive radio waves, which functions as the antenna.
On a surface of the outermost base among the bases, a shielding conductor pattern may be formed so as to be exposed to the outside. In plan view, the shielding conductor pattern may be disposed on the conductor patterns formed on other of the bases.
With such an arrangement, the shielding conductor pattern shields the antenna from radio waves. When transmitting radio waves, no radio waves are emitted in the conductor pattern direction. The antenna is also shielded from electromagnetic noise from the conductor pattern direction.
A power feeding port may be formed on the surface of the outermost base so as to be exposed to the outside. A connecting section to be connected to another electronic component may be configured by the power feeding port and the shielding conductor pattern.
With such an arrangement, the parts to be connected with another electronic component, namely the power feeding port and the shielding conductor pattern, are coplanar. Hence, the antenna can be mounted on the electronic component at the coplanar surface.
A trimming pattern for trimming the impedance of the entire antenna may be formed on the bases.
With such a configuration, the impedance of the entire antenna can be changed to an arbitrary value by altering the shape of the trimming pattern in accordance with the necessary frequency.
The conducting sections may include through holes formed in the thickness direction of the bases.
With such an arrangement, in plan view, the conductor patterns are configured to be connected at a single point.
Preferably, the bases are protected by a covering while the shielding conductor pattern and the power feeding port are exposed to the outside.
According to the present invention, a small antenna is provided, which can be attached to the interior of a casing of each of various apparatuses, such as portable communication terminals, which have functions of transmitting and receiving radio waves. It is thus not necessary to extend the antenna, and hence the antenna is not easily damaged and the overall appearance is improved. The present invention is particularly advantageous when used in a frequency bands with a long wavelength, such as with the very high frequency (VHF) band and the ultra high frequency (UHF) band. By stacking a plurality of bases, a plurality of resonance modes are obtained by a plurality of capacitance components while the overall length remains the same.
According to the present invention, transmission of radio waves in the conductor pattern direction is blocked. Therefore, the antenna gains in the direction of areas in which the conductor patterns are absent are improved. It is thus possible to increase the transmission distance compared with a case in which no conductor pattern is used. At the same time, the antenna is shielded from noise from a radio transmitting and receiving circuit. It is thus possible to directly mount the antenna on a circuit board, allowing more freedom in choosing the mounting location. This is advantageous in that the antenna can be attached to the interior of a casing of each of the apparatuses having functions of transmitting and receiving radio waves.
According to the present invention, a connection section can be connected with solder to another electronic component, such as a printed board forming a radio transmitting and receiving circuit. This allows space saving when attaching the antenna to the interior of a casing of each of various apparatuses having functions of transmitting and receiving radio waves. The present invention is advantageous for trimming the impedance between a resonant system and a radio transmitting and receiving circuit system to be connected to the resonant system. When connecting a plurality of conductor patterns, no space is necessary. This is advantageous for the reduction of the outer dimensions. An exposed surface can be used as a mounting surface to be mounted on a transmission circuit board. Once the antenna is mounted, effects of oxidation of the conductor patterns and damage caused by external forces on radio transmission and reception are minimized.